J. S. R O B I N S , C. E. N E L S O N AND C. E. D O M I N G O2
Over-irrigation is a m a j o r p r o b l e m in m a n y i r r i g a t e d areas. On the new l a n d s in t h e C o l u m b i a Basin Project, most of t h e soils have relatively h i g h w a t e r h o l d i n g capacities a n d infiltration rates. A p p l y i n g irrigation water too frequently a n d for excessive d u r a t i o n s on these soils has made this p r o b l e m particularly acute.
In a d d i t i o n to c o n t r i b u t i n g to d r a i n a g e p r o b l e m s in the area, over- irrigation may, by leaching, materially affect t h e response of crops to fertilizers. T h i s is especially t r u e of n i t r o g e n , w h i c h is the n u t r i e n t most c o m m o n l y deficient in these soils.
T h e effects of over-irrigation in the area have b e e n most noticeable in sugar beet p r o d u c t i o n because of the l o n g irrigation season, the high nitrogen r e q u i r e m e n t of the crop, a n d the low n i t r o g e n c o n t e n t of the soils in the area. In m a n y fields, this crop has d e v e l o p e d severe n i t r o g e n deficiency symptoms in midseason even w h e r e n i t r o g e n a p p l i c a t i o n s w e r e relatively high.
Most of the r e p o r t e d irrigation a n d n i t r o g e n fertilization work on sugar beets has b e e n designed to d e t e r m i n e e i t h e r the effects of d e p l e t i n g the soil m o i s t u r e to p r e d e t e r m i n e d levels or the effects of n i t r o g e n rates a n d place- m e n t m e t h o d s on yield, sugar c o n t e n t a n d p u r i t y . Some a t t e n t i o n also has b e e n given to certain i n t e r r e l a t i o n s h i p s b e t w e e n soil m o i s t u r e a n d nitrogen fertilization.
L i t t l e evidence exists, however, relative to n i t r o g e n utilization under various c o n d i t i o n s of irrigation practice. T h i s is especially t r u e of prac- tices involving a p p l i c a t i o n of excess irrigation water3.
T h e study r e p o r t e d h e r e was designed to d e t e r m i n e t h e effects of a p p l i c a t i o n of excess irrigation w a t e r on utilization of n i t r o g e n and the r e s u l t i n g effects u p o n sugar b e e t yield, sugar c o n t e n t , a n d n i t r o g e n status.
Certain of the yield a n d w a t e r a p p l i c a t i o n efficiency information has been previously r e p o r t e d (2, 3 )4. T h i s p a p e r presents two season's data p e r t a i n i n g p r i m a r i l y to n i t r o g e n status a n d sugar c o n t e n t of sugar beets as affected by excess w a t e r a p p l i c a t i o n a n d by n i t r o g e n r a t e a n d placement m e t h o d .
1953 Experiments Experimental Procedure
Six e x p e r i m e n t s were c o n d u c t e d in 1953 in t h e C o l u m b i a Basin Project in W a s h i n g t o n . At each site, t h r e e i r r i g a t i o n t r e a t m e n t s were established as follows:
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r1 Contribution from the Western Soil and Water Management Section, ARS, USDA in cooperation with the Washington Agricultural Experiment Stations, the Utah-Idaho Sugar Company, and the Amalgamated Sugar Company. Material financial assistance from the Utah
Idaho Sugar Company and the Amalgamated Sugar Company is gratefully acknowledged
2 Soil Scientist, Agronomist, and Soil Scientist respectively, Western Soil and Water Man
agement Section, ARS, Irrigation Experiment Station, Prosser, Washington. .
3 "Excess irrigation water" as used in this paper refers to irrigation water added in excess
of that which the soil will retain. '
4 Numbers in parentheses refer to literature cited.
V O L . IX, N o . 2, J U L Y 1956 Treatment
Number 1 2 3
Relative Quantity of Water Added per Irrigation
X 2X 3X
181
T h e m a g n i t u d e of the q u a n t i t y " X " was determined from pan evapora- tion measurements (I) in conjunction with plain size and cover. Irrigation 'frequently was d e t e r m i n e d from the quantity " X " and the moisture re-
tention characteristics of the profiles. All three treatments at a given site- were irrigated simultaneously at frequencies of 1-4 to 28 days.
Nitrogen rate sub plots were established in each main irrigation plot by sideclressing a b o u t t h i n n i n g time. These rates were 60, 120, 180, and 360 p o u n d s p e r acre of N at four of the six sites. At the remaining two sites, pre-planting applications of about 120 and 155 pounds per acre of N had been made so the final rates will not conform to the other sites. All nitrogen was a p p l i e d as N H4N O3.
Fifteen to 20 recently-matured petioles were obtained periodically from each plot for nitrogen status evaluations. Two rows 25 to 30 feet in length were harvested for yield and sugar content evaluations.
Results a n d Discussion Effects on yield.
Yield a n d irrigation information for 1953 have been previously reported (2) . Deep percolation losses for the 2X treatment varied from 7 to 20 inches a n d for the 3X treatment from 18 to 39 inches at the- six locations.
Even with deep percolation losses of these magnitudes, no significant yield depressions were a p p a r e n t . As will be discussed later, failure to remove sufficient nitrogen to depress yields is attributed to the fact, that little excess irrigation water was applied early in the growing season.
Effects on sugar content
Results of sugar content determinations at harvest for certain of the 1953 locations are presented in T a b l e 1. No measurable effect of irrigation t r e a t m e n t was noted and in general only the highest nitrogen rate resulted in appreciable depression of the sucrose percentage.
Table 1.—Sugar Content at Harvest as Influenced by the Irrigation and Nitrogen Rate Treatments for Certain of the 1953 Locations.
1 8 2 J O U R N A L OF T H E A. S. S. B. T. ']
Effects on plant nitrogen level
R e s u l t s of total- a n d n i t r a t e - n i t r o g e n d e t e r m i n a t i o n s on p e t i o l e samples are d e p i c t e d in Figures 1 a n d 2 for location 1. All n i t r o g e n levels, except the 360 p o u n d r a t e , were e i t h e r below or a p p r o a c h i n g the critical level of U l r i c h (4) by S e p t e m b e r 3, which was a b o u t seven weeks before harvesting.
T h i s e x p l a i n s the relatively small sugar c o n t e n t differences o b t a i n e d . Of p a r t i c u l a r interest are i r r i g a t i o n - s a m p l i n g d a t e i n t e r a c t i o n s obtained in these m e a s u r e m e n t s . T h e irrigation t r e a t m e n t s receiving excess water h a d the highest n i t r o g e n levels in the beet petioles at the first sampling.
Differences were greatest at the two highest n i t r o g e n rates i n d i c a t i n g that the excess water a p p l i e d p r i o r to t h e first s a m p l i n g d a t e increased the availability of the shallow sidedressed n i t r o g e n . L o w e r n i t r o g e n levels noted on t r e a t m e n t s receiving no excess w a t e r were p r o b a b l y d u e to o n e or both of two factors: (A) Excessive fertilizer c o n c e n t r a t i o n in t h e a r e a of place- m e n t restricting r o o t g r o w t h u n t i l the n i t r o g e n was m o v e d by t h e irrigation water, or (B) Dry soil in the surface layer restricting root activity and n i t r a t e m o v e m e n t .
1954 Experiments Experimental Procedure
In 1954, t h r e e e x p e r i m e n t s were c o n d u c t e d ; two n e a r Moses Lake, W a s h i n g t o n , in the C o l u m b i a Basin Project a n d o n e at T o p p e n i s h , Wash- i n g t o n , in the Yakima Valley. At T o p p e n i s h , the i r r i g a t i o n t r e a t m e n t s were the same as those used in 1953. At t h e two Moses L a k e locations, the fol- lowing irrigation t r e a t m e n t s were established.
Location 1—Moses L a k e T r e a t m e n t
N u m b e r 1 2 3 4 5
Irrigation Frequency
Relative Quantity of Water Added per Unit Time 2 weeks
4 weeks 2 weeks 4 weeks 2 weeks
X X 2X 2X 3X
Location 2—Moses Lake Treatment
Number Irrigation
Frequency
Relative Quantity of Water Added per Unit Time
1 2 3 4 5
Before 7/15 4 weeks 2 weeks 2 weeks 4 weeks 4 weeks
After 7/15 4 weeks 4 weeks 4 weeks 2 weeks 2 weeks
Before 7/15 X 2 X 4 X X X
After 7/15 X X X 2X 4 X
T h e q u a n t i t y " X " was again d e t e r m i n e d from p a n e v a p o r a t i o n m e a s u r e m e n t s (1) , p l a n t size, a n d cover. Since fixed i r r i g a t i o n frequencies were used on different t r e a t m e n t s , the q u a n t i t i e s of w a t e r a d d e d at each irriga- t i o n were d e t e r m i n e d from the i r r i g a t i o n frequency a n d t h e magnitude of
| p V O L . IX, N o . 2 , J U L Y 1936 183
" X " d u r i n g the interval in question. T h e frequencies used were determined from soil moisture r e t e n t i o n characteristics of the profiles and peak con- sumptive use information previously determined.
Figure 2.—Effects of nitrogen and irrigation on nitrate-nitrogen levels beet petioles at location 1, 1953.
Figure 1.—Effects of nitrogen and irrigation on total-nitrogen level of beet petioles at location 1, 1953.
1 8 4 J O U R N A L OF THE A. S. S. B. T.
N i t r o g e n was a p p l i e d at t h r e e rates by each of four m e t h o d s of place- m e n t w i t h i n each irrigation plot. T h e rates, in a d d i t i o n to t h e O N plots, were 120, 240, a n d 360 p o u n d s of N p e r acre; the p l a c e m e n t m e t h o d s were plowed-down, disced-in, shallow sidedressed, a n d d e e p sidedressed. All nitro- g e n was a p p l i e d a s N H4N O3
Fifteen to 20 y o u n g m a t u r e petioles were again o b t a i n e d periodically from each p l o t for n i t r o g e n status evaluations. T w o rows, 20 or 25 feet in length, were harvested for yield a n d sugar c o n t e n t d e t e r m i n a t i o n s .
Results and Discussion Effects on yield
Yield a n d i r r i g a t i o n i n f o r m a t i o n for t h e 1954 e x p e r i m e n t s has been r e p o r t e d previously (3) . Yields were again unaffected by excess irrigation w a t e r at the T o p p e n i s h location, w h i c h received t h e same t h r e e irrigation t r e a t m e n t s as were used in 1953.
T h e irrigation phases of the r e m a i n i n g two locations were designed to study the effects of h i g h e r rates of d e e p p e r c o l a t i o n a n d to c o m p a r e early season a n d late-season a p p l i c a t i o n s of excess water. Yield d a t a for these two locations (1954) are p r e s e n t e d in F i g u r e 3.
M a r k e d r e d u c t i o n s in yield resulted from excess w a t e r applications at b o t h locations. F a i l u r e to o b t a i n such depressions in yield by late excess a p p l i c a t i o n s at location 2 indicates t h a t only the early season applications are i m p o r t a n t in r e d u c i n g yield by leaching of n i t r o g e n . T h i s explains the failure to o b t a i n yield depressions in 1953 a n d at the T o p p e n i s h location in 1954, since no early excess water a p p l i c a t i o n s were m a d e in these cases.